The present invention relates to an earphone unit mounted in the auditory tube (also called auditory canal) or on the ear, which unit comprises voice reproduction means for converting an electric signal into acoustic sound signal and for forwarding the sound signal into the user""s ear, and speech detection means for detecting the speech of the user of the earphone unit from the user""s said same auditory tube. The earphone unit is suitable for use in connection with a terminal device, especially in connection with a mobile station. In addition to above the invention is related to a terminal device incorporating or having a separate earphone unit and to a method of reproduction and detection of sound.
Traditional headsets equipped with a microphone have an earpiece for either both ears or only for one ear, from which earpiece in general a separate microphone bar extending to mouth or the side of mouth is protruding. The earpiece is either of a type to be mounted on the ear or in the auditory tube. The microphone used is air connected, either a pressure or a pressure gradient microphone. The required amplifiers and other electronics are typically placed in a separate device. If a wireless system is concerned, it is possible to place some of the required electronics in connection with the earpiece device, and the rest in a separate transceiver unit. It is also possible to integrate the transceiver unit in the earpiece device.
Patent publication U.S. Pat. No. 5,343,523 describes an earphone solution designed for pilots and telephone operators, in which earpieces are mounted on the ears and a separate microphone suspended from a bar is mounted in front of the mouth. In addition to above, a separate error microphone has been arranged in connection with the earpieces, by utilizing which microphone some of the environmental noise detected by the user can be cancelled and the intelligibility of speech can be improved in this way.
Alternative solutions have been developed for occasions in which a separate microphone suspended from a bar cannot be used. Detection of speech through soft tissue is prior known e.g. from throat microphones used in tank headgear. On the other hand, detection of speech through the auditory tube has been presented in patent publication U.S. Pat. No. 5,099,519. In said patent publication it has been said that the advantages of speech detection through the auditory tube are the small size of the earpiece and the suitability of the device to noisy environment. A microphone closing the auditory tube acts also as an elementary hearing protector.
Patent publication U.S. Pat. No. 5,426,719 presents a device which also acts as a combined hearing protector and as a means of communication. In said patent publication, as well as also in the above mentioned patent publication U.S. Pat. No. 5,099,519, the microphone is placed in one earpiece and the ear capsule respectively in the other earpiece. This means that a device according to any of the two patent publications requires using both ears, which makes the device bulky and limits the field of use of the device.
Patent publication WO 94/06255 presents an ear microphone unit for placement in one ear only. The unit is mounted in a holder for placement in the outer ear. For use in full duplex ear communication the holder further has a sound generator. Between the sound generator and the microphone is mounted a vibration absorbing unit. Also the sound generator is embedded in a thin layer of attenuation foam.
Another device for two-way acoustic communication through one ear is described in patent publication U.S. Pat. No. 3,995,113. This device is based on an electro-acoustic mutual transducing device adapted to be inserted into the auditory canal and which can function both as a speaker and microphone. It forms an ear-plug type transmitting-receiving device. The device additionally includes means for reducing the mechanical impedance of the vibrating system and a means for eliminating the noise resulting from said impedance reducing means.
Now an improved earphone unit has been invented, which unit facilitates placing of a microphone and an ear capsule in same auditory tube or on the same ear and which has means for eliminating sounds produced into the auditory tube by the ear capsule from sounds detected by the microphone. This improves the detection of the user""s speech, which is registered via the auditory tube, especially when the user speaks simultaneously as sound is reproduced by the ear capsule. In telephones, such as mobile phones this is needed especially in double talk situations, i.e. when both the near end and far end speaker speak simultaneously. It is possible to install in the earphone unit also a separate error microphone for elimination of external disturbances. It is possible to use for microphones and ear capsules any means of conversion prior known to a person skilled in the art that convert acoustic energy into electric form (microphone), and electric energy into acoustic form (ear capsule, loudspeaker). The invention presents a new solution for determining the acoustic coupling of a microphone and a loudspeaker and for optimizing voice quality using digital signal processing.
The earphone unit according to the invention is suitable for use in occasions in which environmental noise prevents from using a conventional microphone placed in front of mouth. Respectively, the small size of the earphone unit according to the invention enables using the device in occasions in which small size is an advantage e.g. due to inconspicuousnes. In this way the earphone unit according to the invention is particularly suitable for use e.g. in connection with a mobile station or a radio telephone while moving in public places. The use of the earphone unit is not limited to wireless mobile stations, but it is equally possible to use the earphone unit in connection with even other terminal devices. One preferable field of use is to connect the earphone unit to a traditional telephone or other wire-connected telecommunication terminal device. It is equally possible to use the earphone unit according to the invention in connection with various interactive computer programs, radio tape recorders and dictating machines. It is also possible to integrate the earphone unit as a part of a terminal device as presented in the embodiments below.
When an attempt is made to detect from the auditory tube simultaneously speech of very low sound pressure level and sound is fed with relatively high sound pressure level into the same ear using the ear capsule, problems arise when analogue summing units and amplifiers equipped with fixed adjustments are used. In this system the auditory tube is an important acoustic component, because it has an effect upon both the user""s speech and on the voice produced by the ear capsule. Because the auditory tube of each person is unique, the transfer function between the microphone and the ear capsule is individual. In addition to this the transfer function is different each time the earphone unit is set into place, because the ear capsule may be set e.g. at a different depth. If the setting of the earphone unit is not completely successful, the acoustic leakage of the ear capsule may be beyond control, which can disturb the operation of the device. An acoustic leakage means e.g. a situation in which environmental noise leaks past an ear capsule placed in the auditory tube into the auditory tube. If an earphone unit according to the invention consisting of a microphone and an ear capsule is placed in a separate device outside the auditory tube, it is particularly important to have the acoustic leakage under control.
In order to be able to separate the sound components produced by various sources of noise, which components are disturbing and unnecessary from the point of view of the intelligibility and clearness of the user""s speech and in order to be able to remove them from the signal detected by the microphone in such a way that essentially just the user""s voice remains, the transfer functions between the various components of the system must be known. Because the transfer function between the microphone capsule and the ear capsule is not constant, the transfer function must be monitored. Monitoring of the transfer function can be carried out e.g. through measurements based on noise. In order to improve voice quality and the intelligibility of speech, it is possible to divide the detection and reproduction of speech in various frequency bands which are processed digitally.
It is characteristic of the ear-connectable earphone unit and the terminal device arrangement according to the invention that it comprises means for eliminating sounds produced into the auditory tube by said sound reproduction means from sounds detected by said speech detection means.
It is characteristic of the terminal device according to the invention that said sound reproduction means and said speech detection means have been arranged in the terminal device close to each other in a manner for connecting both simultaneously to one and the same ear of a user, and the terminal device further comprising means for eliminating sounds produced into the auditory tube by said sound reproduction means from sounds detected by said speech detection means.
It is characteristic of the method according to the invention that disturbance caused in the ear by the first sound signal is subtracted from said second sound signal.